1. Field of the Invention
The present invention relates generally to a system for preparing packaging material, and particularly to a compact, self-contained apparatus and method for expanding loose fill material, such as polystyrene pellets, for packaging such articles.
2. Description of the Prior Art
It is well known in the art to use expanded polystyrene pellets as packaging materials for void fill applications and for shipping fragile, oddly shaped or mixed lots of products. In such a packaging system, small dense polystyrene pellets are expanded, much like popcorn, to form large fluffy, loose fill foam material about one hundred times the original size. Such expanded polystyrene loose fill foam may be used to pack substantially any article and protects virtually everything it surrounds.
Polystyrene loose fill packaging provides numerous advantages. For example, the low weight to volume ratio of the material polystyrene provides substantial savings in packed product transportation and shipping costs. The polystyrene pellets neither absorb moisture from the air nor lose their protective qualities when wet, and the snow-white color and resilient surface keep goods clean and scratch free. Further, a polystyrene loose fill packaging system does not produce dust, chips, static electricity, or waste and, since the polystyrene loose fill is stored in overhead hoppers and is gravity fed into shipping cartons, such a system provides substantial savings in packaging time and labor costs.
One alternative to the present system is to purchase expanded, ready-to-use, loose fill material. However, as ready-to-use loose fill is expanded to about 100 times its original size, a substantial portion of the end user cost is then related to the transportation and handling of "air".
For the above reasons, interest in developing a simple, compact, self-contained apparatus for expanding polystyrene loose fill material at the packaging site has recently increased. Typically polystyrene pellets are initially subjected to a preexpansion operation bringing them to a partially expanded state. These partially expanded pellets are then subjected to multiple additional expansions to bring them to their fully expanded state. FIG. 1 illustrates one device which has resulted from this development for performing the multiple subsequent expansions. The device generally comprises a hopper 10 for gravity feeding expandable loose fill material 11 to a cloth-type conveyor belt 12. The belt, e.g. a polyethylene mesh belt, is disposed over steam distributing means 14 and conveys the expandable loose fill material 11 through a steam filled expansion chamber 16 to a discharge chute 18.
While the conveyor belt-type device of the prior art has great utility in many applications, further improvements may still be made to it. The cloth-like conveyor belt of the prior art has particular utility in that the steam released below the conveyor belt may penetrate therethrough by convection. In this manner, the pile of loose fill material conveyed thereacross may be exposed to steam from all sides, facilitating uniform expansion thereof. However, the close weave of cloth-like materials generally traps a portion of the moisture in the steam as it penetrates therethrough, thus restricting the flow of the steam, reducing the exposure of the loose fill material to the steam, and tending to deteriorate the cloth-like material.
In addition, because the loose fill material is gravity fed from the hopper to the conveyor belt, and thereafter remains generally stationary relative to the cloth-like conveyor belt, it tends to form in uneven piles. As the loose fill material expands, these piles often trap a portion of the moisture from the steam and clump together. This causes non-uniform exposure of the loose fill material to the steam, and consequent non-uniform expansion thereof.
Further, due to the fact that the steam rises through the apparatus by convection, and the light-weight loose fill material is gravity fed from a hopper, the steam also tends to force the loose fill material to back up into the hopper, causing clogging.
Finally, because the loose fill material is expelled while still hot and moist from the steam in the expansion chamber, the expanded loose fill material tends at least partially to reshrink.